The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An aircraft is moved by several turbojet engines each housed in a nacelle also housing a set of connected actuating devices related to its operation and performing various functions when the turbojet engine is operating or stopped. These connected actuating devices in particular comprise a mechanical thrust reverser device.
The propulsion assembly of the aircraft formed by the nacelle and the turbojet engine is designed to be suspended from a stationary structure of the aircraft, for example below a wing or on the fuselage, by means of a suspension pylon.
The nacelle generally has a tubular structure comprising an air intake upstream from the turbojet engine, a middle section designed to surround a fan of the turbojet engine, a downstream section housing the thrust reverser means and designed to surround a combustion chamber and the turbines of the turbojet engine, and generally ends with a jet nozzle whereof the outlet is situated downstream from the turbojet engine.
This nacelle may be designed to house a dual flow turbojet engine, i.e., a turbojet engine capable of generating a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine and by means of the rotating fan blades, and a cold air flow (secondary flow) that circulates outside the turbojet engine through a flow tunnel of the cold air flow.
An outer structure called OFS (Outer Fan Structure), housing the thrust reverser means, and an inner structure IFS (Inner Fan Structure), designed to cover a downstream section of the turbojet engine, both belonging to the downstream section of the nacelle, define the flow tunnel of the cold air flow as well as a passage section of the cold air flow.
The thrust reverser device is able, during landing of the aircraft, to improve the braking capacity thereof by reorienting at least part of the thrust generated by the turbojet engine forward. During that phase, it obstructs the flow tunnel for the cold air flow and orients the latter toward the front of the nacelle, thereby generating a counterthrust that is added to the braking of the wheels of the aircraft.
In the case of a so-called cascade reverser, the cold air flow is reoriented by cascade vanes associated with a cowl having a sliding function serving to expose or cover said vanes.
Additional blocking doors, also called flaps, activated by the sliding of the cowl, allow closing of the flow tunnel of the cold air flow, downstream from the vanes so as to allow the reorientation of the cold air flow toward the cascade vanes.
These flaps are mounted pivotably on the cowl sliding between a retracted position, in which they provide, with said moving cowl, the aerodynamic continuity of an inner wall of the outer structure of the nacelle, and a deployed position in which, in the thrust reversal situation, they at least partially close off the tunnel so as to deflect the flow of cold air toward the cascade vanes exposed by the sliding of the cowl.
Traditionally, the pivoting of each flap is guided by connecting rods attached on the one hand to the flap, and on the other hand to a stationary point of the inner structure of the nacelle delimiting the flow tunnel for the flow of cold air.
The installation of such a cascade thrust reverser device on a turbojet engine below the wing is made complex when the maximum nacelle height constraint is critical due to a low ground clearance of the aircraft and a proximity between the turbojet engine and the wing of the aircraft.
Such an installation furthermore involves delicate management of the passage section for the cold air flow.
In the context of this issue, it has already been proposed to place, in an aircraft with low ground clearance, a cascade thrust reverser device by reducing the length of the cascade vanes and increasing the axial air leaks naturally present between the reverser flaps (so as to avoid interference), when they are deployed in the reverse jet of the device, and axial air leaks between each flap and the inner structure of the nacelle delimiting the flow tunnel for the flow of cold air.
The leaks between each flap and the inner structure of the nacelle delimiting the tunnel are even greater when the length of the cascade vanes is reduced so as to preserve substantially the same flow rate of the cold air flow.
This makes it possible to reduce the thickness of the moving cowl and, consequently, the nacelle, which may retain a substantially circular section.
However, the assembling choice for such a device involves a reduced and low reverser efficiency, since the leak flow rate affects the reverser efficiency.
In the context of this issue, it has also been proposed to reduce the height of the nacelle by proposing a nacelle that is not of revolution around the central axis of the turbojet engine, called “flattened nacelle”.
Such a priori flat nacelle has no impact on the reversal efficiency. It is possible to retain the same leakage level as on a reverser in a normal configuration.
In that case, the thrust reverser flaps are of different heights to adapt to the different tunnel height at 12 o'clock (i.e., in the upper part of the nacelle) and at 6 o'clock (i.e., in the lower part of the nacelle), and the connecting rods actuating the thrust reverser flaps have different lengths to ensure that the flaps all pivot with the same angle.
The combination of leakage flaps and flattened nacelle, with no offset kinematics, is therefore feasible with connecting rods of different lengths.